The art of producing glass fibers as a reinforcement for thermoplastic and/or thermosetting resins has long known to coat the fibers with an organic polymer before embedding the coated fibers in the laminating resin. The fibers are most economically coated with the polymers at forming. Because the fibers are formed immediately beneath red hot bushings having orifices therein through which the molten glass passes before solidifying into the fibers, the solidified fibers are best coated with an aqueous emulsion of the polymer in order to avoid a fire hazard. Numerous problems exist in the process of applying a prepolymer to the glass fibers from a water phase. One problem is that the size that is used to coat the fibers contains a high percentage of water which causes migration of the size solids during drying of the coiled packages of the coated fibers. Additional water also requires additional drying, which when accomplished by a gas-fired oven produces additional discoloration of cationic materials. In addition, the silanes which are added to the size slowly hydrolyze on standing, and in doing so agglomerate. The emulsified particles of the prepolymer may also slowly agglomerate on standing, and the coating on the fibers of the agglomerated material usually leaves some areas of the fibers devoid of a coating. When incompletely coated fibers are used as a reinforcement for laminating resin, a poor bond of the laminating resin to the fibers results in certain areas and these areas then breakdown under repeated reversals of stress.